深海棲艦が現れる数年前
江田島の基地に団体見学に来ていた1人の少女が自衛隊にスカウトされるきっかけになった出来事

A few years before the appearance of Abyssal Fleet.
The event that led to one girl who visited the Etajima base for a group tour to be scouted by the Self-Defense Forces.